The uptake of tritiated norepinephrine in isolated rabbit mesoduodenal blood vessels was measured. Neuronal uptake was estimated utilizing the inhibitory effect of cocaine, and expressed on the basis of wet and dry tissue weights as well as circumferential area of the vascular wall. This area was presumed to approximate the area of the adrenergic nerve terminal plexus. The wet weight of smaller tissues was apt to be underestimated due to excessive drying during weighing; dry weight was more consistent over a wide range of tissue size. Either on the basis of weight or circumferential area, neuronal uptake in arteries increased as the diameter diminished, but uptake was practically constant in all segments of the veins. Arterial uptake per unit circumferential area was greater than in the accompanying veins, but this was not necessarily the case when uptake was expressed per unit weight. Neuronal norepinephrine uptake may be a useful index of adrenergic nerve density. On this basis it is suggested that the adrenergic neural vasoconstriction increases with decrease in diameter of both arteries and veins in rabbit mesoduodenum.